Method of making heat exchangers



March 7, 1939.

H. s.. HOLMES METHOD OF MAKING HEAT EXCHANGERS 6 Sheets-Sheet 1 Filed March 13, 1936 I March 7,1939. I H. s. HOLMES METIjODOF MAKING HEAT EXCHANGERS Filed March 13, 1936 6-Sheets-Sheet 2 ATTORNEYS Mai-ch 7, 1939. s. HOLMES 2,1-49;696

METHOD OF MAKING HEAT EXCHANGERS Filed March 13, 1936 a Sheets-Sheet s INVENTOR.

ATTORNEYS HEN/PmSJE/OLMQS'.

March 7, 1939. H. s. HOLM'ES METHOD OF MAKING HEAT EXCHANGE-RS 6 Sheets-Sheet 5 Filed March 15, 1956 7 v \xis TOR I B fiE/YRYJfi L M55".

ATTORNEYS Patented Mar. 1, 1939 PATENT- OFFICE rmmon ormma nna-r nxcnisasas Henry 8-. Holmes, mum N. 1.. assignor to tropolitan Engineering Company, Brooklyn. N. Y.,' a corporation of New York Application March 13, v1936, Serial No. 66,605

scum.

In boilers providing steam or hot water for the heating of houses, it'is common to use fire tubes or passages enclosed within a water chamber, the hot gases of the furnace passing through such tubes so as-to heat the water.

The-present invention aims to provide a boiler in which tubes of this general character are of improved construction having a considerably enlarged heating surface; so that they 'may be fewer or smaller than the plain tubes which have heretofore been used. The invention also includes certain heat exchangers useful in boilers and. various other applications; and. also a method of producing them.

The accompanying drawings illustrate an emthe fire tubes. Figs. 3 and 4 are respectively horizontal sections on the lines 3-4 and l-4 of Fig. 2. Fig. 5 is an end view of one of the fire tubes before installation. Figs. 6, 7, 8, 9 and 10 illustrate successive steps ina method of producing such tubes. Fig. 11 illustrates amodification of Fig. 6. Figs. 12, 13, 14 and 15 are crosssections illustrating different methods of forming such tubes. Fig. 16 is an end view of a strip which is to be formed into a tube by the method of Fig. 15. Figs. 17 and 18 are respectively a cross-section of a methodpf forming another style of tube and an end view of such a tube. Figs. 19 to 22 illustrate partly and completely an alternative form of tube; Fig. 19 be n a perspec- 5 tiveof atubular segment; Fig. 20a perspective of the complete tube; Fig. 21 an elevation of the same. and Fig. 22 a section on the line 22-42 of Fig. 21.

, Referring first to Figs. 1, 2 and 3. the boiler 4o-has a shell I extending from top to bottom and Gas or oil burners would normally be- 5 placed at the bottom of the combustion chamber formed by the inner casing 3. At the top is a coupling Sfor the steam or hot water outlet, and at the bottom a coupling I for the'return pipe bringing condensed steam or feed water. Tubul- 55 lar couplings 8; and 9 serve for attachment of pressure gauge andpressure regulator. Various 'otheri attachments and common details are asw The furnace has an arched portion l0-at the. so 1 front and an-arched portion ii at the rear, these the lower tier of tubes l3 and the similarly contwo being connected by a vertical plate l2 extending across thev furnace from rightto left. Into plate i2 are swaged or otherwise connected the rear ends of fire tubes I} which extend forward to a smoke box it normally covered at the 5 front end, thecover being removable to facilitate cleaning. The back wall I! of the smoke box carries the swaged or welded forward ends of nected forward ends of an upper tier of fire tubes it which lead entirely through the water chamber to the back of the boiler into a smoke hood I! whence the flue gases are conducted in any usual or suitable way to a stack or chimney.

In order to increase the eficiency of such fire 15 tubes for use in this and in various other types of boiler and other heat exchangers. I propose to make these tubes of a special construction by which an increased heating surface is secured for a given size and number of tubes.' These are 20 made of sheet metal with inwardprojectlons. welded to the inner face. While such tubes are specially useful because of their compactness in boilers and the like, they arealso useful as heat exchangers in various other apparatus. Several 2:, methods of producing such tubes are illustrated in Figs. 5 to 22.

Referring to Figs. 5 and 6, the shell of the tube is made of two strips of sheet metal ill of semicircular shape welded together along'edges i9. 30 Projections 2ll/are welded to the inner faces of the strips and extend into the interior; Themethod of production is as follows: 7

A flat sheet i8, Fig. 6, has the projections 20 welded to one face of it, ,The projections are arranged in lines "so as to constitute a'sort of longitudinal fins on the faceof the strip. But each of the projections is fairly small in crosssection and isseparately welded to the strip, thus avoiding strains which occur from the heat of 40 welding continuous fins of substantiallength.

There are three such fins or lines of projections shown in Fig. 6, but the number may be suited to the size and proposed use. The length of the projections is such as-to extend nearly to the cen- 4t ter of the tube so that they practically or nearly cover the entire diameter and thus utilize the stream of hot gas throughout practically its entire cross-section; transmitting the heat rapidly through the welded joint to the shell of the tube and thence tothe water outside.

The projections are so grouped as to leave opentransverse spacesfi extending clear across the strip and also to leave clear transverse spaces 22 at the ends. The strip of Figs.- 6 and 7 is bent down into a hollow shape such as the illustrated semi-cylindrical segment by means of a die 23, Fig. "8, having a semi-circular recess and a punch 2!. the underface of which is shown in Fig. 9. It has semi-circular projections 25 on so .strips l8. Two of such semi-cylindrical segments are brought together as in Fig. 5 and may be welded accurately and quickly by resistance welding between suitable electrodes. Qr various other methods of welding may be utilized.

The projections 20 instead of being in a line parallel with the sides of the strip, and ultimately with the central axis of the tube, may be set in oblique lines as in Fig. 11, leaving clear transverse spaces 2| as before for part of a punch. A tube made of such strips will differ from Fig. 5 only in that the lines of projections will be spiral instead of truly axial and will thus tend to secure better contact with the stream of hot gas.

Fig. 12 shows another method of pressing the strip I8 with its projections 20 into 'the die 2:. The punch 29 is provided with along rib 30 which engages the central line of projections 20 and pushes these and consequently the entire strip l8 down into the die.

According to Fig. 13 the punch 3i difiers in that it has a rib 32 in the lower end of which is a slot that accommodates the center line of I projections 20 while pressing the strip l8 down into the semi-circular die.

Fig. 14 illustrates an extension of the idea of Fig. 13,- using a punch 33 which has a rib 34 with a rounded enlargement 35 on the end having a slot for the central line of projections II, the sides of the enlargement 35 being cut away to permit the bending in of the projections 20 at the sides. This has the advantage of giving a curved bearing face on-the inside of the work during the bending operation.

Figs. 15 and 16 show how the punch and die of Fig. 14 may be usedto make atub which is composed of a single stri'pof metal". The strip is made of a width corresponding substantially to the entire circumference of the tube. It has five lines of projections 20. The central one is engaged in the slot in the enlargement 35 at the lower end of the die. The upper part of the rib 34 is sufiiciently small to permit the ends of the strip 36 to be bent nearly together. a The strip before being inserted is of the hollow shape shown in Fig. 16. The central portion is left flat 'with the three corresponding projections 20 standing upright. The ends are curved around about a quarter circle. The strip is then intro-1 duced into the die and punched as in Fig. 15 to the hollow, nearly tubular, shape there illustrated. The punch is then withdrawn.

In this case, as in Fig. 14, the punch -must be withdrawn lengthwise of the tube because of the interference of the bent-in projections 20 at the sides. The strip 36 is then pressed between elec-- trodes to bring its two free edges together and to weld them so as to form the complete tube.

The shape of the tube in cross-section is not necessarily circular. Rectangular shapes have some advantage in compactness and may be used where the pressures involved are not suilicient to distort the cross-section.

According to Fig. 1'! a strip 31 is made with three rows of projections and is then bent down inadie38 bymeansoi'apunch ahavingarecess in the lower end to accommodate the projections; thus bending the strip into a t or hollow shape of channel form. Two such segm ments 3! are united by means of welded edges ll and will have the projections 20 extending in parallel directions from two opposite walls of the tube nearly to the center thereof.

In the designs of Figs. 12, 13. 14, '15 and 17 it is not necessary to leave transverse (such as 2|, Figs. 6 and 11) for punch segments; therefore, pins 20 may be provided in continuous rows and as close together as required.

The strip may be first formed up into a semicylindrical or other segment of a tube before welding in the projections; subsequently uniting the tubular segments, as explained; In that case, the pro ctions may be differently shaped and arranged since there is no necessity for leaving spaces to accommodate a bending pimch.

' Figs. 19 to 22 illustrate such a tube and the method of production. One of the hollow semicircular segments ll, Fig. 19, is provided with projections 42 which are in the form of inclined bailles, parallel to each other so as to leave between them an oblique channel 43.

It will be understood that a number of such bailies and channels are provided according to the lengthof the tubeflfThebames arecurvedat their rear edges to fit the curved segment ll and have their outer edges lying in a diametral plane. Two such strips with baflles welded within than are placed together as in Fig. 20, 'one being inverted end for end with reference to the other so that the bailles at one side will be as indicated at 42 and those at the other as indicated at l2. The segments are then'welded together as at M. The gases will thus travel along the tube continuously forward .first in the channel between two bailles 42 at one side and then (dividing into two streams) between the bullies I! at the opposite side; andso on throughout the length of complete the tube. This arrangement'secures a wiping ofthe faces ofthebaflesbythehptgu and forces the latter 'intq a aig-zag which the stream is divided agai and 'alfl Various other modifications in detail may h madbbythoseskiiledintheartwithmitdepcrtingfromtheinventionasdefinedinthell pended claims.

Various modifications may be made by those skilledintheartwithoutdepartingtromtheinvention as defined in the following claims.

What I claim is: 1. The method of making a heat the character described which comprises-welding projections along the length of a strip of sheet metal, leaving open transverse spaces, bending said strip to hollow form with the projections extending inward by pressure against the strip at said open transverse spaces ,and welding the edges of such strips together.

. 2. The method of making a heat-exchanger of the character described which comprises welding projections along the length of a strip of sheet metal to form discontinuous longitudinally exwas tending ribs, bending said strip to a hollow form with the projections extending inwardly by applying pressure against said strip between said projections and longitudinal edges oi such strip to form a hollow structure. 

